High-accuracy coupled-cluster computations of bond dissociation energies in SH, H_2S, and H_2O

摘要

The first and second bond dissociation enthalpies of H_2S have been investigated at up to the CCSD(T)/aug-ccpV6Z level of theory corrections for core/valence electron correlation, anharmonic zero point vibrational energy and relativistic effects were followed by extrapolation to the complete basis set limit. Analysis of direct dissociation yields D_0(S-H) = 349.9 and D_0(HS-H) = 375.8 kJ mol~(-1). Together these imply an atomization enthalpy for H_2S about 1 kJ mol~(-1) larger than literature evaluations. consideration of exchange of a second H atom fro mOH to SH yield D_0(HS-H) = 376.2 kJ mol~(-1). The two computations of D_0(HS-H) lie within 0.5 kJ mol~(-1) of a recent spectroscopic measurement of D_0(HS-H) = 376.24 kJ mol~(-1) [R. C. Shiell, X. K. Hu, Q. J. Hu, and J. W. Hepburn, J. Phys. Chem. A 104, 4339 (2000)]. The deuterated analogs SD and D_2S are also considered. There is also accord to within 1.5 kJ mol~(-1) with D_0(S-H) = 348.4 +- 0.8 kJ mol~(-1), which we derive from the experimental literature. We propose revised enthalpies of formation, #DELTA#_fH_0(~2#PI#_(3/2)SH) = 142.6+-0.8 kJ mol~(-1) and #DELTA#_fH_(298.15)(SH) = 143.1+-0.8 kJ mol~(-1). The results suggest the dominant uncertainties in these high-level calculations come from the basis set extrapolation and scalar relativistic terms, and that both contribute about 1 kJ mol~(-1) uncertainty We also obtain D_0(H-OH) = 492.6 kJ mol~(-1), which compares well with recent experiments.